Systems for processing of substrates such as, for example, semiconductor wafers or photovoltaic wafers, glass substrates for photovoltaic products, FPD (Flat Panel Display) products or CCD (Charge-Coupled Device) products or reticles comprise in most cases a plurality of system component stations to which or from which the substrates are transported by means of a robot. System component stations are, for example, storage containers for substrates, also called cassettes, or stations for manufacturing processes such as etching, vaporization, coating, rinsing, drying, exposing, cleaning, heat treatment, etc. Also, in the processing system, transfer points can be present which require depositing the substrate and picking it up again. For this purpose, means for supporting the substrate are provided, such as gripper arms, support columns, support pins, transfer pins, clamping or suction means which are necessary for the handling of the substrates and which come into mechanical contact with the same.
Due to the high sensitivity of the substrates, in particular with respect to a mechanical damage and surface contamination, and due to the high material value of the substrate, high precision robot systems are used for movement and for the transport of the substrates, and the handling itself is carried out exclusively under clean environmental conditions. To avoid chemical reactions of the substrate, in particular of oxidation processes, it is further known to perform, to some extent, the loading and unloading of processing stations from or into cassettes filled with substrates in an inert atmosphere. For this purpose, the chamber in which the processing station or a transfer station, the substrate container, and the robot are arranged is filled with an inert gas, for example with a noble gas or nitrogen.
The robot system for the transport of the substrates has to carry out precise movements and has to ensure the gripping, transporting, and depositing of substrates with high reliability. To prevent mechanical damage to the substrate surface, an exact positioning, aligning and parallelizing of the substrate relative to the devices in the processing systems is necessary. For gripping a substrate, its location or position in space must be known exactly to avoid the danger of unintended scratching of the substrate surface or also of another component of the substrate processing system. The latter could result in that material particles are scraped off from a mechanically damaged component of the substrate processing system and pollute or contaminate the substrate surface or another device of the substrate processing system. Further, a precise aligning of the substrate is important so that the substrate does not slide during the transport. If this is the case, the substrate could slide against another component, for example an arm or a holding member, and the surface could get scratched. A damage to the substrate results in its uselessness.
For a reliable, precise gripping, positioning, and depositing of the substrates in the substrate processing system, the knowledge of their exact position or of the spatial position of the pick-up and depositing positions of suitable means such as, for example, cassettes or suction or clamping means of a processing station is an essential prerequisite. Even fractions of a millimeter can result in an incorrect gripping, positioning, or depositing of the substrate and can cause damage.
It is known to specify the location position of the individual substrates at first manually or to take it over from drawing data, in particular CAD drawings. However, a specified substrate position must be maintained at all times which is rarely ensured in practice. Further, through wear of the moving parts in the processing system, the tolerances become gradually larger. This leads to the situation that the gripper grab of the robot does not grip the substrate accurately any more. Further, maintenance, repair work, modifications or new arrangements of processing stations require a new recording of the substrate positions for the access of the robot grab, which can result in high down times, and in case of a local intervention in contamination of the latter.
It is further known to perform the recording of the substrate positions in an automated manner. For this, substrate-like sensor carriers are used, i.e., sensor carriers which have the shape of the substrates to be transported and/or to be processed. This has the advantage that the sensor carrier can be treated in the processing environment like a normal substrate. Sensor carriers of this type have a height of less than the vertical spacing of two substrates in a cassette and have the dimensions of the planar substrates, in case of wafers to be processed, for example, a diameter of 150 mm, 200 mm, or 300 mm. Such sensor carriers can be stored in a conventional substrate storage container and can be used as required by the robot system for measuring the substrate positions. The manual intervention of a technician in the substrate processing system can hence be avoided.
Such a substrate-like sensor carrier is known, for example, from WO 03067183 A2. This sensor carrier uses an optical camera, by means of which a picture is taken of a target object, or of a substrate, respectively, the position of which is to be measured. Based on this picture, the location position in space of the substrate is calculated. The disadvantage of this system is that reference points must be available on the substrate object to be measured, which reference points must subsequently be looked for in the taken picture. Another disadvantage of this method is that an optical camera and a suitable image evaluation system is needed, which results in increased cost of the sensor carrier and in a high complexity of the same. Finally, it is also a disadvantage that the substrate object to be imaged must always be illuminated to allow an evaluation of the taken picture.